Trick-or-treaters can expect to enjoy temperatures up to 19C (66.2F) on Halloween after heavy rain batters Britain over the next few days.
Weather forecasters have warned that several bands of rain will move across the country before the mercury rises on the spookiest night of the year.
The Environment Agency has issued 21 flood warnings in Wales, the South West, the Midlands and the North East, while more than 50 less serious flood alerts are in place across England and Wales.
MeteoGroup said up to 1.2in (30mm) of rain could fall in some local areas in northern and eastern parts of the UK on Wednesday, as well as the South West of England on Thursday night.
The weather is set to improve on Halloween, when London is expected to record the country's highest temperature of 19C (66.2F) - well above the average of 14C (57.2F) for the time of year but below last year's record of 23.6C (74.5F).
The South of England is expected to reach 15C-18C (59F-64.4F) on Halloween, while conditions will be cooler across the rest of the country with highs of 13C-16C (55.4F-60.8F) in the North of England and 12C-15C (53.6F-59F) in Scotland.
Andy Ratcliffe, a forecaster with MeteoGroup, said: "It will remain unsettled for the next couple of days. Heavy rain will push north west across eastern parts of the UK today.
"Overnight, a band of rain will push into the south, before another band of rain comes from the west.
"On Thursday, initially there could be some heavy bursts of rain before it becomes more fragmented and stays mainly in the west.
"Another band of rain will push from the south through Thursday night, which will bring more heavy bursts. The rain will be heaviest in the South and South West. The north will escape most of the rain.
"On Friday, the rain eases across England and Wales but another band of rain pushes into western areas later.
"The weekend will be dry generally with high pressure coming from the South East. The North West will continue to see rain at times."